Finger lever of a valve train of an internal combustion engine

ABSTRACT

The invention proposes a finger lever ( 1 ) of an internal combustion engine, said finger lever ( 1 ) being switchable to different valve lifts for at least one gas exchange valve and comprising an outer lever ( 2 ) having two arms ( 3   a   , 3   b ) between which an inner lever ( 6 ) is arranged for pivoting relative to the outer lever ( 2 ), which outer and inner levers ( 2, 6 ) can be coupled to each other by a coupling element ( 15 ) so that, upon coupling, a high valve lift, and upon uncoupling, a low valve lift is generated, the finger lever ( 1 ) further comprising on one end ( 7 ), a support (( 8 ) for a gas exchange valve, on an opposite end ( 4 ), a complementary surface ( 9 ) for a support element and on at least one of the outer and inner levers ( 2, 6 ), a contact surface ( 14 ) for a cam. In the finger lever ( 1 ) of the invention, the outer lever ( 2 ) is configured to transfer a high cam lift and the inner lever ( 6 ) is configured to transfer a low cam lift, and only the inner lever ( 6 ) comprises a rotatable roller acting as said contact surface ( 14 ) while each arm ( 3   a   , 3   b ) of the outer lever ( 2 ) comprises a sliding contact surface acting as a cam contacting surface. In this way, a switchable finger lever ( 1 ) is provided in which only that part of the lever comprises a roller acting as a contact surface ( 14 ) that is predominantly activated during the operation of the internal combustion engine. In the present case, this is the inner lever ( 6 ).

FIELD OF THE INVENTION

[0001] The invention concerns a finger lever of a valve train of an internal combustion engine, said finger lever being switchable to different valve lifts for at least one gas exchange valve and comprising an outer lever having two arms between which an inner lever is arranged for pivoting relative to the outer lever, which outer and inner levers can be coupled to each other by a coupling element so that, upon coupling, a high valve lift, and upon uncoupling, a low valve lift is generated, the finger lever further comprising on one end, a support for a gas exchange valve, on an opposite end, a complementary surface for a support element and on at least one of the outer and inner levers, a contact surface for a cam.

BACKGROUND OF THE INVENTION

[0002] In a finger lever of the pre-cited type disclosed in DE-OS 27 53 197, the inner lever cooperates with a high-lift cam and the outer lever cooperates with a pair of low-lift cams. The surfaces for contacting the cam are sliding contact surfaces. A drawback of this prior art is that the sliding contact surfaces unnecessarily increase friction in the valve train.

[0003] It is usual, in general, in finger levers of the pre-cited type to equip only the inner lever with a roller that constitutes a contact surface for the cam and to provide a sliding contact surface on the arms of the outer lever. Generally, the inner lever cooperates with a high-lift cam and the outer lever is contacted by a low-lift cam and possesses, for example for reasons of design space, only sliding contact surfaces on the arms. However, empirically or statistically seen, the switchable finger lever is switched for 80 to 90% of the operating time of the internal combustion engine to the low lift so that it is the outer lever that is activated. Thus the relatively low-friction roller contact is availed of only for a short period of operation. This means that for a major portion of the operation period, the inner lever comprising the roller as a cam contacting surface executes a lost motion and the roller with its comparatively large mass oscillates unnecessarily in the valve train.

OBJECT OF THE INVENTION

[0004] The object of the invention is therefore to provide a finger lever of the pre-cited type in which the aforesaid drawbacks are eliminated.

SUMMARY OF THE INVENTION

[0005] According to a first solution, the invention achieves the above object by the fact that only that one of the outer and inner levers that, empirically or statistically seen, predominantly transfers the cam lift to the gas exchange valve during the operation of the internal combustion engine comprises a rotatable roller acting as a cam contact surface.

[0006] Alternatively, according to a second solution, the invention achieves the above object by the fact that the outer lever is configured to transfer a high cam lift and the inner lever is configured to transfer a low cam lit, and only the inner lever comprises a rotatable roller acting as a cam contacting surface while each arm of the outer lever comprises a sliding contact surface acting as a cam contacting surface.

[0007] In this way, the aforesaid drawbacks are effectively eliminated. It is understood that further features of the invention that will be described below can be incorporated in both solutions. It is also conceivable to achieve only a zero lift through the inner lever so that the valve is de-activated, or to achieve a minimum lift.

[0008] Thus, only that lever that during normal operation of the internal combustion engine predominantly transfers the cam lift comprises the roller acting as a cam contacting surface. Preferably, this lever is the inner lever and the roller is preferably mounted on the pin through a rolling bearing such as a needle roller bearing. Sliding contact surfaces are provided as cam contacting surfaces on the arms of the outer lever for the high-lift cam. In this way, a low-friction cam contact is achieved in the main operation range of the internal combustion engine (low load to part load) in which only a small valve lift is desired.

[0009] According to a further feature of the invention, one end of the inner lever comprises the support for the gas exchange valve and the opposite end of the inner lever comprises a complementary surface for mounting on a preferably hydraulic support element. This complementary surface can particularly be configured as a cup-shaped recess on the inner lever. This enables a simple pivoting motion of the finger lever on the support element.

[0010] The coupling element is constituted by slides, not specified more closely, that can be displaced in at least one axial direction, for example hydraulically, electromagnetically or by the force of a compression spring. According to a still further proposition of the invention, an axial line of the slide coincides with an axial line for the roller in the inner lever. It goes without saying that the slides can likewise extend outside of an axial line of the roller. In place of the slides, it is also conceivable to use other coupling elements like latch- or ball-type elements and the like.

[0011] According to another proposition of the invention, in a region of the end of the inner lever comprising the support, the inner lever projects clearly beyond an end of the outer lever. In this way, the outer lever is configured only with a length that is absolutely necessary. This reduces the mass as well as the cost of manufacture of the finger lever.

[0012] A still further proposition of the invention concerns a simple connection of the inner lever to the outer lever. A pin or a similar component extends through the inner lever in a region of the opposite end, and the outer lever is pivotally mounted through its arms on this pin. Advantageously, at least one torsion spring acting as a lost motion spring is also arranged in the region of this pin. This torsion spring is supported at one end on a crossbar that connects the arms of the outer lever and, at another end, this torsion spring acts on a stop of the inner lever that is configured, for instance, as a pin and arranged on an outer wall of the inner lever. If necessary, other lost motion springs like coil springs and the like may also be used. It is also possible to mount the outer lever on the inner lever by other means, for example, through socket-like supports or a forked engagement.

[0013] If at least one part of the finger lever is made of a light-weight material like sheet metal or fiber-reinforced plastic, a further contribution is made to reducing both the weight and the oscillating mass of the valve train.

[0014] The invention will now be described more closely with reference to the appended drawing.

BRIEF DESCRIPTION OF THE DRAWING

[0015]FIG. 1 is a three-dimensional view of a finger lever of the invention,

[0016]FIG. 2 is a top view of the finger lever of FIG. 1,

[0017]FIG. 3 shows a section taken along line III-III of FIG. 2, and

[0018]FIG. 4 shows a section taken along line IV-IV of FIG. 2.

DETAILED DESCRIPTION OF THE DRAWING

[0019]FIG. 1 discloses in a three-dimensional representation, a finger lever 1 of the invention. This finger lever 1 comprises an outer lever 2 having two arms 3 a, 3 b that are connected to each other in the region of one (opposite) end 4 of the finger lever 1 by a crossbar 5 oriented toward a cam. An inner lever 6 extends between the arms 3 a, 3 b for pivoting relative to the outer lever 2. In the region of one end 7, the inner lever 6 comprises a support 8 for a gas exchange valve (see the other figures as well). In the region of the end 4, the inner lever 6 comprises on an underside, a complementary surface 9 for support on a head of a preferably hydraulic support element.

[0020] As can be seen further, a cross-pin 10 extends through the inner lever 6 in the region of the end 4. In the region of this end 4, the outer lever 2 comprises on each side a bore 11 into which ends 12 of the cross-pin 10 extend.

[0021] Two torsion springs 13 acting as lost motion springs are arranged between the inner lever 6 and the outer lever 2 as viewed in transverse direction. These springs surround the cross-pin 10 on both sides of the inner lever 6 and act at one end against the crossbar 5 and at the other end against a stop 14 a that projects laterally outward from the inner lever 6. In the de-activated state of the finger lever 1 (low lift), a permanent contact of the outer lever 10 with the cam is thus assured.

[0022] Approximately in the region of a central transverse plane, the inner lever 6 comprises a rotatable roller that acts as a contact surface 14 for a low-lift cam. An axial line of this roller is aligned to an axial line of a coupling element 15 (see particularly FIG. 4) for selectively connecting or separating the outer and inner levers 2, 6. The outer lever 2, in contrast, comprises on its cam-proximate side on each arm 3 a, 3 b a sliding surface acting as a cam contacting surface. Since, during the operation of the internal combustion engine, the finger lever 1 operates mainly in the low-lift mode and is thus in an uncoupled state, only the inner lever 6 that cooperates with the low-lift cam comprises a rolling-bearing mounted roller acting as a contact surface 14.

[0023] For further advantages of the invention, reference is made to the introductory description of the invention. 

What is claimed is:
 1. A finger lever of a valve train of an internal combustion engine, said finger lever being switchable to different valve lifts for at least one gas exchange valve and comprising an outer lever having two arms between which an inner lever is arranged for pivoting relative to the outer lever, which outer and inner levers can be coupled to each other by a coupling element so that, upon coupling, a high valve lift, and upon uncoupling, a low valve lift is generated, the finger lever further comprising on one end, a support for a gas exchange valve, on an opposite end, a complementary surface for a support element and on at least one of the outer and inner levers, a contact surface for a cam, wherein only that one of the outer and inner levers that, empirically or statistically seen, predominantly transfers the cam lift to the gas exchange valve during operation of the internal combustion engine comprises a rotatable roller acting as a cam contact surface.
 2. A finger lever of a valve train of an internal combustion engine, said finger lever being switchable to different valve lifts for at least one gas exchange valve and comprising an outer lever having two arms between which an inner lever is arranged for pivoting relative to the outer lever, which outer and inner levers can be coupled to each other by a coupling element so that, upon coupling, a high valve lift, and upon uncoupling, a low valve lift is generated, the finger lever further comprising on one end, a support for a gas exchange valve, on an opposite end, a complementary surface for a support element and on at least one of the outer and inner levers, a contact surface for a cam, wherein the outer lever is configured to transfer a high cam lift and the inner lever is configured to transfer a low cam lift, and only the inner lever comprises a rotatable roller acting as a cam contacting surface while each arm of the outer lever comprises a sliding contact surface acting as a cam contacting surface.
 3. A finger lever of claim 2, wherein the inner lever comprises, on the one end, the support for the gas exchange valve and, on the opposite end, the complementary surface for the support element, a fulcrum of the outer lever being situated in a region of the complementary surface.
 4. A finger lever of claim 3, wherein the coupling element is constituted by at least one transversely extending slide whose axial line is aligned to an axial line of the roller acting as a contact surface in the inner lever.
 5. A finger lever of claim 4, wherein, in a region of the one end comprising the support, the inner lever projects clearly beyond an end of the outer lever, the roller acting as a contact surface being situated approximately in a region of a central transverse plane of the inner lever.
 6. A finger lever of claim 3, wherein the complementary surface of the inner lever is configured as a cup-shaped recess.
 7. A finger lever of claim 3, wherein, at the opposite end, ends of a cross-pin project beyond the inner lever, on which ends, the arms of the outer lever are mounted through their fulcrums formed by a bore in each of the arms.
 8. A finger lever of claim 7, wherein, in a region of the opposite end, the arms of the outer lever are connected on a cam-proximate side by a crossbar, said crossbar being surrounded at least on one side between the outer and the inner lever by at least one torsion spring acting as a lost motion spring that acts at one end against the crossbar and at another end against a stop of the inner lever. 